1. Field of the Invention
The present invention relates to a technique to measure a thickness of a film formed on an object, technique to measure spectral reflectance of an object and a technique to inspect foreign material on an object.
2. Description of the Background Art
Conventionally adopted, as a method of measuring a thickness of a thin film formed on a surface of an object, is ellipsometry, or reflectance spectroscopy or a method which is called a white-light interferometric method without involving ellipsometry (hereinafter, these two methods are referred to as “white-light interferometric method and the like”). In general, the ellipsometry allows a film thickness measurement with high precision on a thin film and the white-light interferometric method and the like allow a measurement on a thicker film, as compared with the measurement by ellipsometry, or on a multilayer film.
Japanese Patent Application Laid Open Gazette No. 61-182507 discloses a method of specifying a thickness of a film on an object from a refractive index which is measured by an ellipsometer and an interfering wave which is obtained by an interferometer, where the ellipsometer and the interferometer are provided in one apparatus.
Japanese Patent Application Laid Open Gazette No. 11-271027 proposes a method for measuring a film thickness, where a range of thickness of a film on an object is specified by the white-light interferometric method and the like and the film thickness is measured by ellipsometry on the basis of the specified film thickness range.
In ellipsometry, however, since a wavelength and an incident angle of light emitted to an object is used in computation for obtaining a film thickness, it is necessary, for high-precision film thickness measurement, to precisely specify the wavelength of an incident light, keep a measurement surface of the object horizontal and so on. Further, since a measurement region is very small, when a microscopic foreign material (e.g., submicron particles) is attached to the surface of the object, it is impossible to perform a film thickness measurement with high precision.
On the other hand, in the white-light interferometric method the like, it is necessary to correct a measured value by using a reference object whose reflectance is known, and if the reflectance is changed due to natural oxidation of a surface of the reference object, it is impossible to appropriately correct the measured value.